In an audio power amplifier for driving a loudspeaker, when a power supply of the amplifier is turned on/off, a strange transient noise, such as a pop noise, may be generated by an audio transient signal in the loudspeaker. To avoid such transient noises, in some solutions, a noise suppressing circuit is provided at an output terminal of the audio power amplifier, which avoids output transient noise resulted from component properties of an output circuit between the audio power amplifier and the loudspeaker.
However, existing noise suppressing circuits are designed based on analysis of an output circuit. There are various types of audio power amplifier, such as class A, class B, class AB, class D, class G and class H, which have different output circuits between the audio power amplifiers and loudspeakers. Besides, some audio power amplifiers do not have an output circuit. For example, a class G audio power amplifier can be directly connected with a loudspeaker. Therefore, the existing noise suppressing circuits, which have complicated circuit design, have limited application scopes.